Biomedical sensors, such as those that utilize enzyme electrodes, can be used to determine the concentrations of a wide variety of analytes and the like rapidly and with considerable accuracy. For example, glucose sensors having enzyme electrodes suitable for in vivo use are typically prepared by depositing a glucose sensitive enzyme, such as glucose oxidase, onto an electrode via an electromotive plating process. Sensors having enzyme electrodes are used, for example, to detect a number of well known analytes such as glucose, urea, uric acid, various alcohols, and a number of amino acids.
Biomedical sensor configurations currently in use typically require a minimum of one polymeric membrane at the interface with the in vivo environment. This membrane which interacts with the in vivo environment in which the sensor is placed can serve a number functions. For example, such membranes can function to limit diffusion, e.g. of glucose, while maintaining high oxygen permeability. In addition, such membranes can function to provide a biocompatible interface with the surrounding tissue.
The introduction of a foreign material such as a sensor into the body, however, typically results in protein deposition or fouling at the surface of the material or device. In particular, following the deposition of protein at the surface, a new surface is essentially created. This new surface influences the temporal sequence of events associated with the healing process. In the context of a sensor, shortly after the injury initiated by implantation of the sensor, cells such as monocytes arrive at the material surface and can differentiate into macrophages soon thereafter. Macrophages are potent generators of damaging chemicals that aid in the process of phagocytosis. These chemical entities and by-products can include hydroxyl radical, superoxide, and strong acids, which may diffuse through the membrane to the underlying enzyme layer. The accumulation of bodies and reagents at the boundary between the sensor and the material to be sampled can introduce noise and interfere with sensor performance.